A pneumatic tire is a polymeric composite and typically contains scores of ingredients, each of which are added to achieve a specific function and overcome a problem. A frequent problem in making a rubber composite is maintaining good adhesion between the rubber and the reinforcement. A conventional method in promoting the adhesion between the rubber and the reinforcement is to generate a resin in-situ (in the vulcanized rubber/textile matrix) by compounding a vulcanizable rubber stock with a phenol/formaldehyde condensation product, The components of the condensation product consist of a methylene acceptor and a methylene donor. The most common methylene donors include N-(substituted oxymethyl) melamine, hexamethylenetetramine or hexamethoxymethylmelamine. A common methylene acceptor is a dihydroxybenzene compound such as resorcinol. Resorcinol is known to form a resin network within a rubbery polymer by reacting with various methylene donors. Unfortunately, the use of resorcinol has some inherent disadvantages. Resorcinol is not readily dispersed in rubber and in fact neither the resin, nor the resorcinol become chemically bound to the rubber. Additionally, resorcinol in its raw form is excessively volatile and is potentially an environmental hazard. Therefore, there exists a need to find a suitable resorcinol replacement.
In silica filled rubber stocks, silane coupling agents are commonly used. Silane coupling agents are in principle characterized by dual functionality. One function is an organo-functional group (such as aminoalkyl, mercaptoalkyl, etc.) and the other functional group is a readily hydrolyzable alkoxy group (such as OCH.sub.3 or --OC.sub.2 H.sub.5). In use, the alkoxy groups readily hydrolyze in the presence of moisture typically found on the surface of silica to form silanols that react with or otherwise condense in the presence of silica surface. The organo functional group reacts with the polymer matrix during vulcanization. In sulfur cured elastomers, mercaptosilanes are odoriferous, usually from impurities in the product. Mercaptosilanes also can act as cure accelerators and may tend to make the rubber compound scorchy. Because the alkoxy groups of the coupling agents readily hydrolyze upon storage, they are not as reactive. Therefore, there exists a need to find a suitable replacement for silane coupling agents.
Surprisingly, the present invention includes the use of phenoxyacetic acid in a rubber stock. The phenoxyacetic acid may function as a replacement for silane coupling agents and resorcinol without imparting any undesirable properties to the rubber stock.